Treatment of phosphoric acid to recover alkali metal fluosilicates

ABSTRACT

Alkali fluosilicates can be recovered from wet process phosphoric acid without contaminating the acid with additional anions, by reacting phosphoric acid with an alkali metal salt, such as sodium chloride, to form the corresponding alkali metal phosphate; extracting the mixture with an organic amine, to remove the contaminating anion; reacting the resultant phosphate solution with wet process phosphoric acid to precipitate an alkali metal fluosilicate, and separating the fluosilicate, thereby leaving residual phosphoric acid. Both the phosphoric acid and the fluosilicate are substantially free of contaminating anion. A portion of the treated phosphoric acid can be recycled for reaction with additional alkali metal salt.

i 6 United States Patent 1 m1 3,714,336 Barker Jan. 30, 1973 541TREATMENT OF PHOSPHORIC ACID 3,493,336 2 1970 Milling ..23 |07 ToRECOVER ALKALI METAL 3,462,242 8/1969 Barker et a1 FLUOSILICATES3,506,394 4/1970 Okamura et al. 3,554,694 1/1971 Barker et a1 ..23/88[75] Inventor: James E. Barker, Freehold, NJ. [73] Assignee: CitiesService Company, New York, Primary Examiner-Edward Stem AttorneyRichardl. Geaman Filed: Aug. 14, 1970 [21] Appl' 63,949 Alkali fluosilicatescan be recovered from wet process phosphoric acid without contaminatingthe acid with [52] U.S. Cl. ..423/321, 423/313, 423/317, additional n s,by reacting phosphoric acid with an 423 341 423 431 alkali metal salt,such as sodium chloride, to form the [51] lm, Cl C01b 25/22, COlb 25/16,C011 33/32 corresponding alkali metal phosphate; extracting the [58]Field of Search ..23/88, 165, 107, 154; 423/321, mixture with an organicamine, to remove the con- 423/313, 317, 341, 481, 488 taminating anion;reacting the resultant phosphate solution with wet process phosphoricacid to [56] References Cited precipitate an alkali metal fluosilicate,and separating the fluosilicate, thereby leaving residual phosphoricUNITED STATES PATENTS acid. Both the phosphoric acid and thefluosilicate are 2,162,657 6/1939 Wehrstein ..23/107 Substantially freeof contaminating anion- A Portion of 2,174,158 9/1939 Kepfer ..23/107the treated phosphoric acid can be recycled for reac- 5, 10/1963 Lobdell23/154 X tion with additional alkali metal salt. 3,393,044 7/1968Blumberg et al. ..23/107 3,186,809 6/1965 Kreevoy ..23/154 X 6 Claims,N0 Drawings TREATMENT OF PHOSPHORIC ACID TO RECOVER ALKALI METALFLUOSILICATES BACKGROUND OF THE INVENTION proved method of recovering analkali metal fluosill0 icate from wet process phosphoric acid (WPA) bytreating WPA with an alkali metal phosphate to precipitate the alkalimetal fluosilicate. In a preferred embodiment, the alkali metalphosphate is prepared by the addition of an alkali metal salt tophosphoric acid, extracting the solution with an immiscible organicamine to remove the protonated anion. The thusformed solution of alkalimetal phosphate in phosphoric acid can then be added to wet processphosphoric acid to precipitate alkali metal fluosilicate. The resultingphosphoric acid is characterized by a reduced concentration offluosilicate and other anions. This invention is an improvement over theprocess described in my earlier U. S. Pat. No. 3,462,242.

Wet process phosphoric acid (WPA) is produced by the acidulation ofnaturally occurring phosphate materials, such as phosphate rock whichordinarily contains about 4 percent by weight of combined fluorine.

Numerous processes for reducing the fluoride concentration of WPA havebeen developed. These include precipitation and filtration of thefluorides, steam or air stripping of the fluorides and simpleconcentration of the acid, in the course of which volatile fluorides areevolved. One prior art practice is to volatilize about half of thefluorine as SiF during the concentration of the primary acid to thefinal merchant grade. This tetrafluoride is collected and converted tofluosilicic acid by scrubbing the volatilized gases with water. Theresulting dilute fluosilicic acid is reacted with an alkali metal oralkaline earth metal salt or hydroxide to form a fluosilicateprecipitate which is recovered by filtration and is washed and dried.This process is inefficient in that only about half of the fluorinevalue is recovered, and the scrubbers required to prevent excessivepollution are expensive and complicated. An alternate method proposedincludes the addition of an alkali metal carbonate, hydroxide orphosphate to the WPA to precipitate the alkali metal fluosilicate. Inthis latter method, however, the resulting alkali fluosilicate iscontaminated with gypsum and other insoluble materials from the acid,requiring subsequent purification by digesting soluble materials withfluosilicic acid. Additionally, in precipitating the fluorine valuesfrom WPA by the addition of alkali, the phosphoric acid is neutralizedto some extent, producing unwanted alkali phosphate. To keep theformation of alkali phosphate to a minimum, a stoichiometric amount ofalkali is added to the wet process phosphoric acid in quantitiessufficient to precipitate substantially all of the fluosilicate. Thisprecipitate, as obtained by prior art techniques, is extremely difficultto separate from the acid because it is quite gelatinous, has a low rateof crystal growth and a slow settling rate.

In these processes, however, the use of chemicals such as hydroxides,carbonates and phosphates results in higher operating expenses. When theless-expensive naturally occurring alkali metal salts are used, theresultant phosphoric acid filtrate contains undesirable anions,contaminating the acid for certain applications and thus rendering itless useful. By the practice of this invention it is possible to employthe alkali metal salts to remove an alkali metal fluosilicate from wetprocess acid and leave a phosphoric acid solution substantially free ofcontaminating anions.

SUMMARY OF THE INVENTION As indicated, an improved treatment ofphosphoric acid for the recovery of alkali metal fluosilicates withoutcontaminating the acid with additional anion has been found. Thisimproved treatment comprises the steps of (a) reacting an alkali metalsalt with clarified phosphoric acid, (b) contacting the resultingphosphoric acid solution, which contains the alkali metal phosphate andthe protonated anion, with an immiscible organic amine, to remove theanion without substantially altering other characteristics of thephosphoric acid solution, (0) contacting the phosphate solutionresulting from step (b) with wet process phosphoric acid, to precipitatean alkali metal fluosilicate, and (d) separating the supernatantphosphoric acid solution from the fluosilicate precipitate.

This process for recovering a metal fluosilicate from dilute wet processphosphoric acid by using some common salts is accomplished withoutcontaminating the phosphoric acid system with the anion of these addedsalts. ln contradistinction to the prior art teaching of the directaddition of a metal salt to the wet process phosphoric acid toprecipitate the metal fluosilicate, this improved process ischaracterized by the treatment of clarified phosphoric acid with analkali metal salt to form an alkali metal phosphate solution andthereafter contacting this solution with an immiscible organic amine oran anion exchange resin to selectively extract contaminating anions fromthe solution. The resultant alkali metal phosphate solution, having areduced content of contaminating anion, is-then contacted with WPA, toprecipitate the alkali metal fluosilicate. Both the fluosilicate productand the resultant phosphoric acid from this treatment are characterizedby a significantly reduced content of contaminating anion.

As used herein, the term anion means the anion component of the alkalimetal salt added to the phosphoric acid. Thus, if sodium nitrate isadded, the nitrate ion is the anion that is selectively extracted fromthe acidic mixture. The term anion does not include the phosphate ion.

As used herein, the term clarified phosphoric acid refers to phosphoricacid from which no alkali metal fluosilicate will precipitate uponaddition of an alkali metal salt.

Although a variety of alkali metal salts is useful within the scope ofthe present invention, economics of the overall process dictate that theless expensive salts are preferable. Any of the common alkali metals,including lithium, sodium, potassium, rubidium and cesium, can be usedin this process. However, sodium and potassium are preferred due totheir wider occurrence and availability. Sodium is particularlypreferred because sodium fluosilicate has a very broad range ofcommercial uses. For the anionportion of the salt, halides, such aschloride, bromide and iodide, and nitrate and sulfate ions can be used.Other anions can be used, provided that the protonated form be morereactive toward the amine extractant than is phosphoric acid since, inthe acid form, these anions react with the amine extractant and are thuseffectively removed from solution. The alkali metal chlorides arecommercially available compounds, and chloride is therefore thepreferred anion, although other halide ions, as well as nitrate andsulfate, can be used. Thus, such inexpensive and readily availablealkali metal salts as sodium chloride and potassium chloride areparticularly preferred.

The clarified phosphoric acid to which the alkali metal salt is addedcan come from any convenient source, and its composition can vary over arather substantial range. Thus, furnace acid as well as WPA can be usedand the P,O, content can range from about 5 percent to about 62 percentby weight. When WPA is used, alkali metal fluosilicates must first beremoved. Such compounds can be removed by precipitation and filtration,and the clarified acidic filtrate then contacted with additional alkalimetal salt, with extraction of protonated anion by an immiscible organicamine being the subsequent step. in another preferred embodiment, wetprocess acid that has previously been clarified as described (contactedwith a sodium phosphate solution, followed by removal of thefluosilicate precipitate,) can be used as the acid source.

The concentration of the clarified phosphoric acid to which the alkalimetal salt is added can vary over a wide range, such as from a low ofabout 5 percent to a high of about 62 percent by weight of P A 5 percentconcentration is somewhat dilute and requires additionalprocessing, suchas removal of water, of the final solution. A 62 percent concentrationis characteristic of the product obtained from the oxidation ofphosphorus and hydration of the resulting P,0,. A feed acid of thisconcentration is. preferably diluted for better reactivity. it isgenerally more convenient to employ a phosphoric acid having a P,O,concentration of from about to about 35 percent, since a 15 percentconcentration is not so dilute as to require extensive processing.Further, when the concentration rises above about percent P,O,, thesolubility of both monosodium phosphate and alkali metal salt in theacid decreases.

The alkali metal salt and the clarified phosphoric acid can be combinedand mixed in any convenient manner. The amount of salt used is thestoichiometric amount needed to furnish cation concentration necessaryto form the fluosilicate precipitate. in a preferred embodiment themixing of these reactants is accomplished by mixing in the presence ofthe amine extractant, as is the case when a mixer-settler arrangement isemployed. For example, the solubility of KCl in 30 per cent I50, acid isabout 6 percent. Thus, if the salt, acid and amine extractant are mixedtogether, the amine reacts with the HCI formed, promoting thedissolution of additional salt. The alkali metal salt can be added invarious physical forms. For example, solid alkali metal salt having aparticle size in the general range of from about 325 mesh to about meshcan be added to the acid. If the particles are much finer than 325 mesh,dusting problems arise. If the particles are larger than about 20 mesh,the rate of solution of the salt-in the acid is lowered, thus limitingthe throughput. In another embodiment, a slurry of salt and water can beadded to the mixer-settler apparatus, wherein the action of the amineextractant in removing the protonated anion encourages dissolution ofthe salt particles. If concentrated phosphoric acid is used, an aqueoussolution of the salt can be added, simultaneously introducing the saltand diluting the acid so that it is able to hold more alkali metalphosphate in solution.

The temperature at which the alkali metal salt and the clarifiedphosphoric acid can be contacted is not critical and can vary over arather broad range. Thus, the temperature can range from about 30 toabout 215 F., preferably from about to about F. It is obvious that, as ageneral rule, at lower temperatures the reaction will be somewhatsluggish while at higher temperatures one may encounter problems ofcorrosion and/or undesirably vigorous reaction. 7

Following the reaction of alkali metal salt with clarified phosphoricacid, the reaction mixture is contacted with an immiscible organicamine, to selectively extract the anion. A wide variety of amineextractants can be used in this extraction process. These extractantsare, in general, secondary or tertiary amines, particularly thosecontaining hydrocarbon groups of approximately six to 24 carbon atoms,such as tricaprylamine and l-dinonylamino-2-dodecanol. The amines aregenerally aliphatic in character although they may be partiallyaromatic. The aliphatic hydrocarbon groups can be straight chained orbranch chained, saturated or unsaturated. In addition, it is possible touse amines containing one or more branch chained alkyl groups and/or oneor more straight chained alkyl groups. Typical amines which may be usedfor this purpose can be represented by the following formula:

NH I in which R is as above described and R is the group:

CH;,C-CCH C=CCH CH3 on.

Compounds of this type are readily available on the market.

The above amine extractants are liquid. In another embodiment of thisinvention, the extractant can be present in the form of an anionexchange resin, in which amine groups are attached to a resin backbone.Such exchange resins are stable solids and can be used in bed form. Suchuse eliminates phase separation operations encountered with the liquidamines.

Additionally, many amine compounds which are suitable within the scopeof this invention will be immediately apparent to those skilled in theart. The nature of the amine employed is not critical. However, theamine is desirably oil soluble and both the amine selected and its saltsshould be water insoluble, since they are employed in a water-immiscibleorganic phase. In general, the total carbon content of the amine canvary from about 22 to about 60 carbon atoms, in which at least one chaincontains from about six to about 24 carbon atoms.

Insofar as the selected liquid amine and its salt are compatible withmany organic solvents, the selection of a diluent for the amine isprimarily a matter of convenience. Kerosene has been found to be ahighly satisfactory solvent. However, the diluent canbe selected from awide variety of materials such as aromatic, naphthenic or aliphatichydrocarbons, or a chlorinated solvent or other nonreactive solvent suchas chloroform, benzene and the like.

The quantity of the amine employed can vary over a broad range. Thepreferred amount of amine is that which will react stoichiometricallywith the anion formed. Excess amine will react with phosphoric acid,resulting in loss of phosphate values. If less than the stoichiometricamount of amine is used, some of the protonated anion will not beremoved, leaving contaminating anions in the solution. When dispersed ina solvent, the amine concentration can vary broadly from as low as 1percent to as much as about 99 percent, preferably from about to aboutpercent. If the amine concentration is much lower than 10 percent, theincreased dilution requires more and/or larger sized equipment for agiven throughput. If the concentration is much over 20 percent, physicallosses of the amine increase.

Subsequent to extraction, the amine extractant can be regenerated with abasic medium, such as sodium carbonate, sodium hydroxide, ammoniumhydroxide or even dry ammonia gas. It is frequently convenient to use alime or magnesia slurry. From an economic consideration, a slurry oflime and water is particularly desirable to regenerate the free amine,which can be recycled for further extraction. The brine obtained onregenerating the organic amine with lime and water is usually discarded.

There are various methods available for contacting the amine extractantwith the alkali metal phosphate solution. One of the more convenientmethods is countercurrent extraction, preferably using more than onestage for more complete extraction. These contacting techniques are wellknown and will not be described further.

One embodiment of this invention is the addition of an alkali metalsalt, such as sodium chloride, to a stream of clarified phosphoric acid,to form a solution of an alkali metal phosphate in phosphoric acid and aprotonated anion such as hydrogen chloride. This mixture is thenextracted by an amine compound, such as an immiscible organic amine oran anion exchange resin. The protonated anion in the mixturepreferentially reacts with the amine extractant, with the resultantimmiscible amine-anion reaction product being effectively removed fromthe phosphoric acid solution. The resultant solution of alkali metalphosphate and phosphoric acid characterized as having a formulaapproximating MH PO,' H P0,,, where M is the alkali metal, is then usedto contact a stream of raw wet process phosphoric acid, the alkali metalphosphate reacting with the fluosilicate in the WPA stream to form ametal fluosilicate which precipitates. The supernatant phosphoric acid,which is readily recovered, and the fluosilicate precipitate both havereduced chloride ion content.

The fluosilicate precipitate will typically be in the form of a settledmud which is conveniently passed to a classifier, filter and drier, toresult in a commercially acceptable alkali metal fluosilicate product.The clarified acid which has been removed from the fluosilicateprecipitate can, of course, in one embodiment be recovered as a product.in another embodiment, however, part of the clarified acid is removedand recycled in the process. Thus, a portion of the clarified acid iscombined with a metal salt such as sodium or potassium chloride. Thesolution so obtained can be selectively extracted as described above toremove residual anion in the form of, for example, hydrogen chloride,which is extremely corrosive in further processing and lowers the gradeof the final product if not removed. The treated acid solution can be berecycled for treatment with the WPA.

Subsequent to extraction, the immiscible phases can readily beseparated. The acidic alkali metal phosphate solution can be recycledfor mixing with raw WPA to precipitate the fluosilicate as describedherein. The organic amine phase can be contacted with a basic strippingagent, as described, to remove the acid form of the contaminating anion.

In one embodiment of the invention, wet process phosphoric acid is fedinto a reactor, together with a phosphoric acid-alkali metal phosphatesolution obtained as described above. The wet process acid and thealkali metal phosphate-phosphoric acid solution are continuallyagitated, stirred or mixed by conventional means. in a preferredembodiment, agitation is characterized by a Reynolds number from about7600 to about 8300 as taught in my earlier U. S. Pat. No. 3,462,242,which teaching is incorporated by reference herein.

Where the agitation is characterized by a Reynolds number below 7600,there is insufficient and inadequate mixing of the reactants.Alternatively, where the agitation is above about that characterized bya Reynolds number of 8300, it is found that the particle size is finerthan is desirable and that difficulty is encountered during subsequentseparation. The precipitate of alkali metal fluosilicate, when formed ata more severe mixing rate, is extremely difficult to filter and purify.

The temperature maintained during mixing is generally in the range fromabout F. to about 200 F., with the range of from about l40 F. to about160 F. being preferred. Below about 100 F., the reaction rate forforming the fluosilicate is lower than the rate at the preferredtemperature. n the other hand, at 200 F. certain components of theacidic mixture, for example HF, can be expelled, leading to airpollution and reducing the yield of the fluosilicate. The mixture can beretained in the mixer for a period of from about minutes to about 2hours, preferably from about to about 30 minutes. The mixing time isgenerally inverse 1y proportional to the mixing temperature. Anuncooperative combination of parameters, such as agitation speed,temperature, concentration of reactants, etc., can lead to an extendedretention time, whereas a favorable combination can produce a desirableprecipitate in a few minutes. The resulting slurry, containingprecipitated alkali metal fluosilicate, is discharged from the mixer,with the solid alkali metal fluosilicate collected by sedimentation andprocessed further according to well known methods. The clarifieddefluorinated phosphoric acid solution can be removed and withdrawn forfurther processing or can be recycled, in whole or in part, fortreatment with an alkali metal salt as described above. Thus, a portionof the clarified defluorinated acid can be combined with an alkali metalsalt in the manner discussed above.

Following extraction of the contaminating anion, the solution of alkalimetal phosphate in phosphoric acid, having a reduced content ofcontaminating anion, can be used directly to manufacture fertilizers orit can be recycled for contact with raw wet process acid. Theamine-kerosene phase can be washed with water to remove water-solublecomponents from the extractant. Following water washing the amine can beregenerated by treatment with a water slurry of calcium oxide, theaqueous solution of calcium chloride being discarded. The regeneratedamine phase can then conveniently be again washed to removed any lasttraces of calcium chloride and calcium oxide and recycled forfurther usein the extraction.

DESCRIPTION OF THE PREFERRED EMBODlMENTS' EXAMPLE 1 One ton of wetprocess phosphoric acid, containing 29% P 0 0.18% chloride, 0.59% Si and2.4% fluorine was fed, together with 710 pounds of an approximately 17%solution of NaH PO, in phosphoric acid (29% P,O,,) into a reactor. Theretention time and temperature in the reactor were 30 minutes and 140 F,respectively. Agitation in the reactor was equivalent to a Reynoldsnumber of 7800. The solids in the effluent from the reactor were settledfrom the solution. The supernatant clarified phosphoric acid wasseparated and split into two streams. One stream, consisting of 685pounds, was mixed with 63.6 pounds of sodium chloride. This mixture wasthen extracted countercurrently with 3610 pounds of a solution of a 15percent solution of an amine in kerosene, in three stages, the amineshaving the general formula R, R, NH, with R, being an aliphatichydrocarbon group containing a tertiary carbon atom, with alkyl groupsubstituents attached thereto and totalling from 1 l to l4 carbon atomsin the three alkyl groups. R: is a straight chain,

saturated alkyl group containing 12 carbon atoms. A compound such asthis is sold by Rohm and Haas Company under the name of Amberlite LA-Z.The resultant aqueous solution, consisting of sodium phosphate inphosphoric acid, (CI' 0.11 percent), was similar to that fed to thereactor initially. The organic phase was washed'with water and thentreated with 48 pounds CaO in a water slurry. The aqueous solution ofcalcium chloride was discarded. The organic phase was then washed withwater and recycled to the extraction step.

The remaining 2065 pounds of the original supernatant acid contained28.1% P 0 0.57% fluorine (available fluorine values from any source,such as F or SiF,),0.4% sodium, 0.15% Si and 0.16% chloride. Thisproduct can be further processed to make phosphatic fertilizermaterials.

The settled solids were classified with water and the classifieroverflow was returned to the reactor. The classifier solids werefiltered, washed with water and dried, yielding 59.4 pounds of sodiumfluosilicate of 99.4 percent purity 0.1% Cl).

lclaim: l. A process for treating wet process phosphoric acid, whichcomprises:

a. reacting clarified phosphoric acid with an alkali metal salt, inwhich the alkali cation is selected from the group consisting oflithium, sodium, potassium, rubidium and cesium, and the anion of thesalt is selected from the group consisting of nitrate, sulfate,chloride, bromide and iodide, resulting in a solution comprising alkalimetal phosphate, protonated anion of the metal salt and phosphoric acid;b. selectively and stoichiometrically extracting the thus-formedprotonated anion from the above solution in which the extractant is animmiscible organic secondary or tertiary amine, in which at least onealkyl chain contains from about six to about 24 carbon atoms, and theamine is used in an amount to stoichiometrically extract the protonatedanion; contacting the phosphate solution obtained from step (b) with wetprocess phosphoric acid, under mixing conditions characterized by aReynolds number between about 7600 and about 8300, to precipitate analkali metal fluosilicate, and

separating the supernatant phosphoric acid, characterized by a reducedcontent of fluorine value and of contaminating anion.

2. A process according to claim 1 in which the alkali metal salt issodium chloride or potassium chloride.

3. A process according to claim 1 in which the organic amine is asecondary amine having the general formula R, R, NH, in which R, is analiphatic chain containing a tertiary carbon atom and R, is a straightchain saturated alkyl group containing about 12 carbon atoms.

4. A process according to claim 1 in which the supernatant phosphoricacid of step (d)'is recycled for use as the clarified phosphoric acid ofstep (a).

5. A process for producing phosphoric acid and alkali metalfluosilicate, both substantially chloride free, which comprises: g

a. treating clarified phosphoric acid with an alkali metal chloride toform a mixture of alkali metal phosphate, phosphoric acid and hydrogenchloride, with the alkali metal selected from the group consisting oflithium, sodium, potassium, rubidium and cesium,

. extracting the mixture with an immiscible seconalkali metalfluosilicate therefrom, and

d. separating the phosphoric acid from the alkali metal fluosilicate,both being characterized by substantial freedom from chloride.

6. A process according to claim 5 in which the clarified phosphoric acidof step (a) contains from about 15% to about 35% by weight of P 0 thealkali metal chloride is sodium or potassium chloride, and theimmiscible organic amine is a secondary amine having the general formulaR R NH in which R is a tertiary alkyl group containing from ll to about14 carbon atoms and R is a straight chain saturated alkyl groupcontaining about 12 carbon atoms.

1. A process for treating wet process phosphoric acid, which comprises:a. reacting clarified phosphoric acid with an alkali metal salt, inwhich the alkali cation is selected from the group consisting oflithium, sodium, potassium, rubidium and cesium, and the anion of thesalt is selected from the group consisting of nitrate, sulfate,chloride, bromide and iodide, resulting in a solution comprising alkalimetal phosphate, protonated anion of the metal salt and phosphoric acid;b. selectively and stoichiometrically extracting the thus-formedprotonated anion from the above solution in which the extractant is animmiscible organic secondary or tertiary amine, in which at least onealkyl chain contains from about six to about 24 carbon atoms, and theamine is used in an amount to stoichiometrically extract the protonatedanion; c. contacting the phosphate solution obtained from step (b) withwet process phosphoric acid, under mixing conditions characterized by aReynolds number between about 7600 and about 8300, to precipitate analkali metal fluosilicate, and d. separating the supernatant phosphoricacid, characterized by a reduced content of fluorine value and ofcontaminating anion.
 2. A process according to claim 1 in which thealkali metal salt is sodium chloride or potassium chloride.
 3. A processaccording to claim 1 in which the organic amine is a secondary aminehaving the general formula R1 R2 NH, in which R1 is an aliphatic chaincontaining a tertiary carbon atom and R2 is a straight chain saturatedalkyl group containing about 12 carbon atoms.
 4. A process according toclaim 1 in which the supernatant phosphoric acid of step (d) is recycledfor use as the clarified phosphoric acid of step (a).
 5. A process forproducing phosphoric acid and alkali metal fluosilicate, bothsubstantially chloride free, which comprises: a. treating clarifiedphosphoric acid with an alkali metal chloRide to form a mixture ofalkali metal phosphate, phosphoric acid and hydrogen chloride, with thealkali metal selected from the group consisting of lithium, sodium,potassium, rubidium and cesium, b. extracting the mixture with animmiscible secondary or tertiary organic amine, in which at least onealkyl chain contains from about 6 to about 24 carbon atoms, used in anamount to stoichiometrically extract the hydrogen chloride, therebyreducing the chloride content of said mixture, c. contacting theresultant acidic alkali metal phosphate solution with wet processphosphoric acid, under mixing conditions characterized by Reynoldsnumber between about 7600 and about 8300, to precipitate a substantiallychloride-free alkali metal fluosilicate therefrom, and d. separating thephosphoric acid from the alkali metal fluosilicate, both beingcharacterized by substantial freedom from chloride.